Subject: LETHAL R-134a concentrations from evaporator failure
Date: Mon Nov 03 12:38:24 1997 GMT
LETHAL R-134a CONCENTRATIONS IN PASSENGER COMPARTMENTS MAY OCCUR
FROM EVAPORATOR FAILURE
In August 1997, a study was done at the Armstrong laboratory, Wright
Patterson Air Force Base, Dayton, OH. The report, "Human Inhalation of
Halon 1301, HFC-134a and HFC-227ea for Collection of Pharmacokinetic
Data" was authored by A. Vinegar, R. Cook, J McCafferty, M. Caracci, and
The concentration of R-134a being used was extremely low and (then
thought) that nothing bad was going to happen. To quote from the bottom
of page 10 (page 11 if abstract prepended), "Subject #3 was the first
volunteer exposed to
HFC-134a. The exposure concentration was 4000 ppm (0.4% v/v) and was
scheduled to last for 30 minutes with a 5 minute postexposure evaluation
period as was accomplished in the Halon 1301 portion of the study.
Approximately 4.5 minutes into the exposure, the subject lost
consciousness and both pulse and blood pressure dropped to zero."
The test was aborted and medical personnel intervened and revived the
subject. Suppose it wasnt a test in a medical lab, that person would be
The industry, has in general, tried to "coverup" this "problem", often
reporting "Human Subject Faints During Botched Air Force R-134a
Inhalation test". They then go on to theorize that the nurse wiggled the
blood drawing needle and that made the subject "faint". See (on the web)
www.autofrost.com/humanhal2.pdf to download your own copy or call Monroe
Air Tech at 1-800-424-3836 for a copy. Be your own judge. Using "0.4%"
(4000 ppm) parts per million of R-134a vapor in air as the "lethal"
amount, the following calculations were performed on several late model
cars. They assume a bad evaporator leak or rupture, allowing the factory
listed charge amount to escape into the passenger compartment. R-134a is
heavier than air, so if the air is not "stirred" by a fan, heavier
concentrations will be found in low spots and lower in high spots. For
these purposes, we will assume the air is stirred and the concentration
The specific Volume of R-134a vapor at "normal" pressure (from the NIST
Standard Reference Database 23 "NIST THERMODYNAMIC PROPERTIES OF
REFRIGERANTS AND REFRIGERANT MIXTURES") is 3.69 cubic feet per pound
(cf/lb). If you blow off a 1 lb can of R-134a into am empty garbage bag
(sealed), it will occupy 3.69 cubic feet.
SPECVOL134a CF R-134a CHG lb 1 1,000,000 parts
conc. (ppm) = ----------- X ------------- X -------- X
lb Int.Vol CF per million
1998 CAR Interior(CF) lb R134a pass.conc ppm Times lethal
Ford Escort 87 1.75 74,224 18.6
GEO Prism 84 1.7 74,679 18.7
Chevy Cavalier 92 1.5 60,163 15.0
Ford Taurus 101 2.13 77,819 19.5
Ford F150* 80 2.38 109,778 27.4
Toyota Camry 96.8 1.88 71,665 17.9
Ford Mustang 83 2.13 94,695 23.7
Chevy Malibu 98.6 1.75 65,492 16.4
Honda Accord 90.4 1.43 58,371 14.6
Chevy S-10* 80 2 92,250 23.1
Chevy MonteCarlo 96.1 2 76,795 19.2
Olds Cutlass Supreme 95 1.75 67,974 17.0
Buick Skylark 87 2.25 95,431 23.9
BMW 5 Series 93.5 3.27 129,051 32.3
* Estimated, since interior volume was not available
Subject: Re: LETHAL R-134a concentrations from evaporator failure
Date: Tue, 04 Nov 1997 06:11:24 -0600
In article <firstname.lastname@example.org>,
> email@example.com wrote:
> >The test was aborted and medical personnel intervened and revived the
> >Suppose it wasnt a test in a medical lab, that person would be "dead".
> Suppose I am in my car driving down the road and my evap blows it's
> guts out. If I am a person with any sense at all, I roll down the
> window, and I can guarantee you, I do not pas out. Now, if I am
> setting at a red light and the same thing happens, if I sit in the car
> long enough to pass out I am 1)very stupid and 2) such a waste of
> matter in the universe that my passing will not matter.
> >to escape into the passenger compartment. R-134a is heavier than air, so
> >if the air is not "stirred" by a fan, heavier concentrations will be
> >found in low spots and lower in high spots. For these purposes, we will
> >assume the air is stirred and the concentration is uniform.
> Like I said, a window down at 60 mph will do plenty of "stirring".
> Give me a break and go do a radon test on you're home.
The peak evaporator pressures dont occur while driving most of the time.
THey happen 30-45 mins after the car is stopped, from engine heat
"soaking" the condenser which "heat pipes" the refrigerant to the
evaporator (in orifice type systems). The evaporator heats up, and
cannot reject much heat (no fan on), so the pressures rise.. Often to
130-150 PSIG range. A GM "Accordian" style evaporator often fails at 175
PSIG (this info from air shops that had them fail at 175 PSIG under a
pressure test). IN this case the evap fails, and the whole charge ends
up in the car, mostly near the floor. Driver gets in, starts up, left the
air on "recirc" and stirs it up.
If he tries to light a cigarette, depending on the conc, he wont be able
to light his lighter or it will light (green flame), and he will get a
lungfull of Hydrofluoric acid on his first drag from 134a breakdown from
Running the A/C fan on "normal" brings in fresh air and should help out
have some "tips" on dealing with 134a leaking.. --ghg
From: firstname.lastname@example.org (George Goble)
Subject: Re: LETHAL R-134a concentrations from evaporator failure
Date: 25 Nov 1997 15:58:15 GMT
In article <email@example.com>,
Greg Fretwell <JRFC31A@prodigy.com> wrote:
>This whole thread certainly seems to be meaningless. Most of the time an
>evaporator leak would be so gradual that the R134 concentration would be
>virtually nonexistant. If you did have a catastrophic decompression I
>suspect the half pound of oil released would have you opening the windows
>in short order if you didn't wreck the car from the surprise.
I hadn't thought of the surprise factor, fog and oil blowing in the vents.
GM uses "accordian" style evaporators, that have been observed
to fail around 175 PSIG on the bench during leak testing with
In a real car, the highest evaporator pressures occur about 30-45
minutes AFTER you shutoff the engine, whether or not the A/C
was used. Refrigerant generally "migrates" to the coldest spot
in the system. 30 mins after stopping the car, much heat "soaks"
out of the radiator/engine into the A/C condenser causing the
refrigerant to boil and "heat pipes" its way to the evaporator.
Since no air is flowing thru the evaporator, it heats up also
and the pressures go up. These often hit 150 PSIG or so
(hot day + hot engine heat soak). This is real close to the
175 PSIG failure point for accordian evaporators.
If an evaporator were to break, it would probably be then.
After your car is in the garage for the night. When you
get back in, the whole charge (some will have diffused out
depending on many things) is in the passenger cmpt.
Evaporators made of copper tubing wont typically fail
like the accordian types and can stand full high side pressure
(450 PSIG). However, things can happen like expansion valve
nuts can vibrate loose, etc, causing large leaks.
If somebody wants to make some money, there probably is a market
to sell a "mobile" R-134a (all refrigerants) leak detector
that runs off cigarette lighter, like home CO and smoke detectors.
You could get out easily (unless wrecked and pinned in).
Hand held R12/R134a detectors now are about $80 and use a single